This invention relates to a method of and apparatus for molding. More particularly this invention concerns a mold assembly such as is used in the production of glass vessels and the like.
In the production of glass vessels and the like it is common practice to form a gob of glass in molten plastically deformable condition into a parison by means of a so-called preform mold. Thereafter this parison is blow-molded into the finished product in a different finish mold. Since the molten gob of glass or the parison has an extremely high temperature, often in the neighborhood of 200.degree. C., it is necessary to cool the molds used for their formation actively. This means that simple heat dissipation into the ambient surroundings is inadequate adequately to cool the mold and achieve any economically justifiable production speed.
Thus, it is necessary to cool the mold typically by passing a cool fluid over the mold. Arrangements have been suggested for passing water and atomized water in air over the mold, as well as simply by forcing air under pressure through passages in the mold. Such systems are frequently relatively complex so that the bulk added to the mold is considerable. In high-speed installations such arrangements are extremely disadvantageous as the rapid opening and closing of the mold is greatly slowed by the considerable bulk of heavy cooling equipment carried by the mold. Furthermore, when a multipart mold is used the complexities increase greatly.
Another disadvantage of the known cooling systems is that it is very difficult to control the cooling in particular regions of the mold. Particularly when non-round objects are being shaped in the mold is it necessary to insure that all of the portions of the object cool at a differentiated rate in order to prevent uncontrolled wall thickness and/or cracking of the workpiece.
It has been suggested to set up the mold for individual cooling of portions. This arrangement has never worked in practice and has added enormous complexities to the molding system. Furthermore, the known systems invariably are set up in accordance with theoretical computations made according to the mold dimensions, so that any other factors which subsequently show themselves to be of greater or lesser importance cannot be compensated out without complete rebuilding of the system.
Another known disadvantage of the systems in use is that the coolant is frequently directed from outside against the mold in order to cool it. Not only does this external equipment increase the size of the installation, but the noise generated by such a system is invariably very great. In fact such systems frequently are the noisiest part of the whole production process. Furthermore, when a liquid coolant is used in such a manner the high humidity levels created by the boiling-off of the liquid causes associated equipment to rust and disintegrate at a great rate. In addition, such external spraying of coolant is inherently messy.
Prior-art mold arrangements can be seen in U.S. Pat. No. 1,798,136 and in British Pat. No. 1,337,292.